FIG. 1 is an internal structure diagram of an LED driving circuit according to related art.
As shown in FIG. 1, a current LED driving circuit consists of a driving control circuit and a constant current channel group circuit, and the driving control circuit is a logic circuit. The driving control circuit includes serial data ports (wherein, the serial data ports include ports Serial Data Input (SDI), Serial Clock (SCLK), Logic Element (LE), Output Enable (OE) and Serial Data Output (SDO)) and a constant current channel control signal set. The serial data ports are responsible for inputting control signals of a system into the LED driving circuit and outputting the control signals of the system out of the LED driving circuit to control each constant current channel of a constant current channel group circuit to be orderly switched on or switched off through the constant current channel control signal set. Wherein, SDI is a data input signal port, SCLK is a shift pulse signal port, LE is a data latching signal port, OE is a unified enable control signal port of a constant current input interface set, and SDO is a data output signal port. Each constant current channel includes a current input end, a current output end and a signal control end, the current input ends of the constant current channel group circuit are connected to the constant current input interface set, and are used for connecting cathodes of LEDs, the current output ends of the constant current channel group circuit are interconnected to an external pin GND of the LED driving circuit, and the signal control ends of the constant current channel group circuit are connected to the constant current channel control signal set.
FIG. 2 is a diagram of cascading application of an LED driving circuit according to related art.
As shown in FIG. 2, a display control logic circuit and N LED driving circuits connected end to end in series are involved in the cascading application of the current LED driving circuit.
A control signal port of the display control logic circuit is connected to the serial data ports SDI, SCLK, LE, OE and SDO of the LED driving circuits, and controls the display of an LED unit board through transmitted serial data.
The control signal port includes: a serial data output signal port C_SDI, a serial data shift pulse signal port C_SCLK, a latching signal port of serial data C_LE and a serial data enable signal port C_OE. Wherein C_SDI is connected to SDI of the first LED driving circuit, and C_SCLK, C_LE and C_OE are respectively interconnected to SCLKs, LEs and OEs of the N LED driving circuits in a bus way. Every two LED driving circuits are interconnected through SD's and SDOs.
SCLK, LE and OE of the current LED driving circuit are interconnected to the display control logic circuit in the bus way, there are many control signals, a difficulty in the wiring of a Printed Circuit Board (PCB) is high, and an anti-interference capability of the control signals is relatively lower.
The large number of a cascaded LED driving circuits may cause a signal transmission problem, and part A in FIG. 5 shows the output signals of the display control logic circuit, wherein C_SDI is the serial output data port, C_SCLK is the shift pulse signal port, an ascending edge of which acquires serial data in a shift register of the logic circuit, and C_LE is the latching signal port of serial data, an ascending edge of which outputs the data of the shift registers in each controlled LED driving circuit in parallel into the signal control ends of the constant current channels.
Part B in FIG. 5 shows a signal diagram of serial data ports of an LED driving circuit of a final stage shown in FIG. 2 during cascading application. After multiple stages of LED driving circuits are connected in series, a signal SDI received by the serial data input port of the final stage has a time delay T_SDI which is caused by the stage-by-stage accumulation of delays of the logic circuits of the N LED driving circuits; and because SCLK/LE/OE do not have any delay, a data change of SDI occurs to an ascending edge of SCLK, the logic circuit part of the LED driving circuit acquires the data of SDI according to an SCLK signal, and acquires the data into the shift register, but the data at this moment is wrong, which may cause an error of a content displayed by the LEDs.
For the problems of high difficulty in the wiring of the PCB, relatively lower anti-interference capability of the control signals and LED display error, which are caused by large control signal number and serial output data delay, during the cascading application of the LED driving circuit in related art, there is yet no effective solution.